Differences in take-off leg kinetics between horizontal and vertical single-leg rebound jumps

This study aimed to clarify the differences between the horizontal single-leg rebound jump (HJ) and vertical single-leg rebound jump (VJ) in terms of three-dimensional joint kinetics for the take-off leg, while focusing on frontal and transverse plane movements. Eleven male track and field athletes performed HJ and VJ. Kinematic and kinetic data were calculated using data recorded with a motion capture system and force platforms. The hip abduction torque, trunk lateral flexion torque (flexion for the swing-leg side), hip external and internal torque, trunk rotational torque, and the powers associated with these torques were larger when performing HJ because of resistance to the impact ground reaction force and because of pelvic and posture control. Pelvic rotation was noted in HJ, and this was controlled not only by the hip and trunk joint torque from the transverse plane but also by the hip abduction torque. Therefore, hip and trunk joint kinetics in the frontal and transverse plane play an important role in a single-leg jump, regardless of the jumping direction, and may also play a more important role in HJ than in VJ.     

Dynamics of the support leg in soccer instep kicking

Abstract

We aimed to illustrate support leg dynamics during instep kicking to evaluate the role of the support leg action in performance. Twelve male soccer players performed maximal instep kicks. Their motions and ground reaction forces were recorded by a motion capture system and a force platform. Moments and angular velocities of the support leg and pelvis were computed using inverse dynamics. In most joints of the support leg, the moments were not associated with or counteracting the joint motions except for the knee joint. It can be interpreted that the initial knee flexion motion counteracting the extension joint moment has a role to attenuate the shock of landing and the following knee extension motion associated with the extension joint moment indirectly contributes to accelerate the swing of kicking leg. Also, appreciable horizontal rotation of the pelvis coincided with increase of the interaction moment due to the hip joint reaction force on the support leg side. It can be assumed that the interaction moment was the main factor causing the pelvis counter-clockwise rotation within the horizontal plane from the overhead view that precedes a proximal-to-distal sequence of segmental action of the swing leg.     

Effects of changing speed on knee and ankle joint load during walking and running

Joint moments can be used as an indicator of joint loading and have potential application for sports performance and injury prevention. The effects of changing walking and running speeds on joint moments for the different planes of motion still are debatable. Here, we compared knee and ankle moments during walking and running at different speeds. Data were collected from 11 recreational male runners to determine knee and ankle joint moments during different conditions. Conditions include walking at a comfortable speed (self-selected pacing), fast walking (fastest speed possible), slow running (speed corresponding to 30% slower than running) and running (at 4 m · s^?1 ± 10%). A different joint moment pattern was observed between walking and running. We observed a general increase in joint load for sagittal and frontal planes as speed increased, while the effects of speed were not clear in the transverse plane moments. Although differences tend to be more pronounced when gait changed from walking to running, the peak moments, in general, increased when speed increased from comfortable walking to fast walking and from slow running to running mainly in the sagittal and frontal planes. Knee flexion moment was higher in walking than in running due to larger knee extension. Results suggest caution when recommending walking over running in an attempt to reduce knee joint loading. The different effects of speed increments during walking and running should be considered with regard to the prevention of injuries and for rehabilitation purposes.     

Analysis of lower limb internal kinetics and electromyography in elite race walking

Abstract

The aim of this study was to analyse lower limb joint moments, powers and electromyography patterns in elite race walking. Twenty international male and female race walkers performed at their competitive pace in a laboratory setting. The collection of ground reaction forces (1000 Hz) was synchronised with two-dimensional high-speed videography (100 Hz) and electromyography of seven lower limb muscles (1000 Hz). As well as measuring key performance variables such as speed and stride length, normalised joint moments and powers were calculated. The rule in race walking which requires the knee to be extended from initial contact to midstance effectively made the knee redundant during stance with regard to energy generation. Instead, the leg functioned as a rigid lever which affected the role of the hip and ankle joints. The main contributors to energy generation were the hip extensors during late swing and early stance, and the ankle plantarflexors during late stance. The restricted functioning of the knee during stance meant that the importance of the swing leg in contributing to forward momentum was increased. The knee flexors underwent a phase of great energy absorption during the swing phase and this could increase the risk of injury to the hamstring muscles.     

Effect of the racket mass and the rate of strokes on kinematics and kinetics in the table tennis topspin backhand

The purpose of this study was to investigate the effect of the racket mass and the rate of strokes on the kinematics and kinetics of the trunk and the racket arm in the table tennis topspin backhand. Eight male Division I collegiate table tennis players hit topspin backhands against topspin balls projected at 75 balls · min^?1 and 35 balls · min^?1 using three rackets varying in mass of 153.5, 176 and 201.5 g. A motion capture system was used to obtain trunk and racket arm motion data. The joint torques of the racket arm were determined using inverse dynamics. The racket mass did not significantly affect all the trunk and racket arm kinematics and kinetics examined except for the wrist dorsiflexion torque, which was significantly larger for the large mass racket than for the small mass racket. The racket speed at impact was significantly lower for the high ball frequency than for the low ball frequency. This was probably because pelvis and upper trunk axial rotations tended to be more restricted for the high ball frequency. The result highlights one of the advantages of playing close to the table and making the rally speed fast.     

Segmental dynamics of soccer instep kicking with the preferred and non-preferred leg

Abstract

Detailed time-series of the resultant joint moments and segmental interactions during soccer instep kicking were compared between the preferred and non-preferred kicking leg. The kicking motions of both legs were captured for five highly skilled players using a three-dimensional cinematographic technique at 200 Hz. The resultant joint moment (muscle moment) and moment due to segmental interactions (interaction moment) were computed using a two-link kinetic chain model composed of the thigh and lower leg (including shank and foot). The mechanical functioning of the muscle and interaction moments during kicking were clearly illustrated. Significantly greater ball velocity (32.1 vs. 27.1 m · s^?1), shank angular velocity (39.4 vs. 31.8 rad · s^?1) and final foot velocity (22.7 vs. 19.6 m · s^?1) were observed for the preferred leg. The preferred leg showed a significantly greater knee muscle moment (129.9 N · m) than the non-preferred leg (93.5 N · m), while no substantial differences were found for the interaction moment between the two legs (79.3 vs. 55.7 N · m). These results indicate that the highly skilled soccer players achieved a well-coordinated inter-segmental motion for both the preferred and non-preferred leg. The faster leg swing observed for the preferred leg was most likely the result of the larger muscle moment.     

Isokinetic knee extension and vertical jumping: Are they related?

The aim of this study was to examine joint power generation during a concentric knee extension isokinetic test and a squat vertical jump. The isokinetic test joint power was calculated using four different methods. Five participants performed concentric knee extensions at 0.52, 1.57, 3.14 and 5.23 rad?·?s^?1 on a Lido isokinetic dynamometer. The squat vertical jump was performed on a Kistler force plate. Kinematic data from both tests were collected and analysed using an ELITE optoelectronic system. An inverse dynamics model was applied to measure knee joint moment in the vertical jump. Knee angular position data from the kinematic analysis in the isokinetic test were used to derive the actual knee angular velocity and acceleration, which, in turn, was used to correct the dynamometer moment for inertial effects. Power was measured as the product of angular velocity and moment at the knee joint in both tests. Significant differences (P <?0.05) were found between mean (?± s) peak knee joint power in the two tests (squat vertical jump: 2255?±?434W; isokinetic knee extension: 771?±?81W). Correlation analysis revealed that there is no relationship between the peak knee joint power during the vertical jump and the slow velocity isokinetic tests. Higher isokinetic velocity tests show better relationships with the vertical jump but only if the correct method for joint power calculation is used in the isokinetic test. These findings suggest that there are important differences in muscle activation and knee joint power development that must be taken into consideration when isokinetic tests are used to predict jumping performance.     

Hip joint kinetics in the table tennis topspin forehand: relationship to racket velocity

The purpose of this study was to determine hip joint kinetics during a table tennis topspin forehand, and to investigate the relationship between the relevant kinematic and kinetic variables and the racket horizontal and vertical velocities at ball impact. Eighteen male advanced table tennis players hit cross-court topspin forehands against backspin balls. The hip joint torque and force components around the pelvis coordinate system were determined using inverse dynamics. Furthermore, the work done on the pelvis by these components was also determined. The peak pelvis axial rotation velocity and the work done by the playing side hip pelvis axial rotation torque were positively related to the racket horizontal velocity at impact. The sum of the work done on the pelvis by the backward tilt torques and the upward joint forces was positively related to the racket vertical velocity at impact. The results suggest that the playing side hip pelvis axial rotation torque exertion is important for acquiring a high racket horizontal velocity at impact. The pelvis backward tilt torques and upward joint forces at both hip joints collectively contribute to the generation of the racket vertical velocity, and the mechanism for acquiring the vertical velocity may vary among players.     

A biomechanical comparison of dominant and non-dominant limbs during a side-step cutting task

Abstract

Numerous studies have investigated anterior cruciate ligament (ACL) injury risk by examining gender differences in knee and hip biomechanics during a side-step cutting manoeuvre since it is known that ACL injury often occurs during such a task. Recent investigations have also examined lower extremity (LE) biomechanics during side-step cutting in individuals following ACL reconstruction (ACLR). Common research practice is to compare knee and hip biomechanics of the dominant limb between groups but this can add considerable complexity for clinicians and researchers. At this time, it is not known if there is a difference in LE biomechanics between the dominant and non-dominant limb during side-step cutting. Three-dimensional kinematics and kinetics were collected while 31 healthy participants performed five, side-step cutting manoeuvres with the dominant and non-dominant limbs. Knee and hip variables examined are those commonly investigated in ACL injury literature. There were no differences between limbs in all but one variable (knee internal rotation). These results demonstrate that healthy individuals exhibit little side-to-side differences in certain LE biomechanics when performing a side-step cutting manoeuvre. These findings can be utilised by clinicians when conducting dynamic evaluations of their ACLR patients and when developing injury prevention and rehabilitation programmes.     

摆臂技术与短跑成绩的关系

运动员摆臂技术的好坏直接影响着步频步幅以及后蹬力量的大小，同时还影响到身体获得向前的水平速度及身体的协调用力。结合训练实践，运用动力学知识，从摆臂技术与短跑的内在联系入手，阐明了摆臂技术与短跑成绩的关系。     

Lower leg and foot contributions to turnout in female pre-professional dancers: A 3D kinematic analysis

Turnout is a central element of classical ballet which involves sustained external rotation of the lower limbs during dance movements. Lower leg and foot compensation mechanisms which are often used to increase turnout have been attributed to the high incidence of lower limb injury in dancers. Evaluation of dancers’ leg posture is needed to provide insight into the lower limb kinematic strategies used to achieve turnout. The primary purpose of this study was to use 3D kinematic analyses to determine the lower leg and foot compensations that are incorporated by female university dancers to accentuate their turnout. Active and passive external tibiofemoral rotation (TFR) was also measured. A moderate-strong negative relationship was observed between hip external rotation (HER) and foot abduction in the three first position conditions. A moderate negative relationship was found between passive TFR and foot abduction in all first position conditions. Our findings suggest dancers are more likely to pronate, than rotate the knee to compensate for limited HER. Dancers with a limited capacity to pronate may force additional rotation via the knee. Ongoing research would benefit from more in-depth analyses of the foot/ankle complex using a multi-segment foot model.     

Mechanical energy generation and transfer in the racket arm during table tennis topspin backhands

The ability to generate a high racket speed and a large amount of racket kinetic energy on impact is important for table tennis players. The purpose of this study was to understand how mechanical energy is generated and transferred in the racket arm during table tennis backhands. Ten male advanced right-handed table tennis players hit topspin backhands against pre-impact topspin and backspin balls. The joint kinetics at the shoulder, elbow and wrist of the racket arm was determined using inverse dynamics. A majority of the mechanical energy of the racket arm acquired during forward swing (65 and 77% against topspin and backspin, respectively) was due to energy transfer from the trunk. Energy transfer by the shoulder joint force in the vertical direction was the largest contributor to the mechanical energy of the racket arm against both spins and was greater against backspin than against topspin (34 and 28%, respectively). The shoulder joint force directed to the right, which peaked just before impact, transferred additional energy to the racket. Our results suggest that the upward thrust of the shoulder and the late timing of the axial rotation of the upper trunk are important for an effective topspin backhand.     

短跑途中跑支撑阶段支撑腿关节肌肉生物力学特性的研究

采用测力、测角加速度和多机多分辨拍摄技术对短跑途中跑支撑阶段肌肉动力学特征进行关节内力矩的计算与分析。研究表明，运动员踝关节跖屈肌的最大力矩与跑的速度呈显著相关；膝关节的伸肌在接近一半的支撑时间内是做离心收缩，离心收缩肌力矩的峰值要高于向心收缩的肌力矩峰值，离地前20％时刻膝关节屈肌起重要作用；髋关节在支撑阶段存在关节屈伸肌群交替工作，在着地后瞬间有较大的屈肌力矩，在离地前髋关节伸肌起重要作用，支撑阶段下肢关节肌肉快速退让性的离心收缩与主动收缩起同样重要的作用。     

Comparison of lower limb kinetics during vertical jumps in turnout and neutral foot positions by classical ballet dancers

The purpose of this study was to investigate the effect of hip external rotation (turnout) on lower limb kinetics during vertical jumps by classical ballet dancers. Vertical jumps in a turnout (TJ) and a neutral hip position (NJ) performed by 12 classical female ballet dancers were analysed through motion capture, recording of the ground reaction forces, and inverse dynamics analysis. At push-off, the lower trunk leaned forward 18.2° and 20.1° in the TJ and NJ, respectively. The dancers jumped lower in the TJ than in the NJ. The knee extensor and hip abductor torques were smaller, whereas the hip external rotator torque was larger in the TJ than in the NJ. The work done by the hip joint moments in the sagittal plane was 0.28 J/(Body mass*Height) and 0.33 J/(Body mass*Height) in the TJ and NJ, respectively. The joint work done by the lower limbs were not different between the two jumps. These differences resulted from different planes in which the lower limb flexion–extension occurred, i.e. in the sagittal or frontal plane. This would prevent the forward lean of the trunk by decreasing the hip joint work in the sagittal plane and reduce the knee extensor torque in the jump.     

The relationship between leg preference and knee mechanics during sidestepping in collegiate female footballers

This study examined the relationship between leg preference and knee mechanics in females during sidestepping. Three-dimensional data were recorded on 16 female collegiate footballers during a planned 45° sidestep manoeuvre with their preferred and non-preferred kicking leg. Knee kinematics and kinetics during initial contact, weight acceptance, peak push-off, and final push-off phases of sidestepping were analysed in both legs. The preferred leg showed trivial to small increases (ES = 0.19–0.36) in knee flexion angle at initial contact, weight acceptance, and peak push-off, and small increases (ES = 0.21–0.34) in peak power production and peak knee extension velocity. The non-preferred leg showed a trivial increase (ES = 0.10) in knee abduction angle during weight acceptance; small to moderate increases (ES = 0.22–0.64) in knee internal rotation angle at weight acceptance, peak push-off, and final push-off; a small increase (ES = 0.22) in knee abductor moment; and trivial increases (ES = 0.09–0.14) in peak power absorption and peak knee flexion velocity. The results of this study show that differences do exist between the preferred and non-preferred leg in females. The findings of this study will increase the knowledge base of anterior cruciate ligament injury in females and can aid in the design of more appropriate neuromuscular, plyometric, and strength training protocols for injury prevention.     

对我国优秀速滑运动员下肢关节伸屈肌群等速测试的个体研究与分析

运用CYBEX NORM等速测力系统,对两名健将级女子速滑运动员左、右腿髋、膝、踝三关节的屈、伸肌群进行了向心运动形式的肌力测试,并根据需要对左、右腿膝关节还进行了等速离心测试,以便找出两人运动学差异的内在动力学原因,为改进技术提供动力学依据。同时描述了速滑运动员髋关节、膝关节和踝关节的力矩曲线特性,进行深入探讨。测试结果:两名运动员的髋关节肌力发展不平衡;快速运动中,二人膝屈肌的肌力水平较差;二人踝关节伸肌群在适应较快速度收缩能力方面较差。     

The three-dimensional kinetic behaviour of the pelvic rotation in maximal sprint running

The purpose of this study was to investigate the effect of lumbosacral kinetics on sprinting. Twelve male sprinters performed 50 m sprints at maximal effort. Kinematic and ground reaction force data were recorded at approximately 40 m from sprint commencement. A whole-body inverse dynamics approach was applied to calculate joint forces and torques at the hip and lumbosacral joints. The contribution of the hips and lumbosacral joint torques to pelvic rotation was subsequently calculated, with joint force powers indicating the rate of mechanical energy transfer between segments across joint centres calculated for both hip joints. The kinetic analysis indicated that the lumbosacral torsional torque contributed significantly to pelvic rotation. Additionally, the pelvic rotation exerted anterior–posterior joint forces on the hips, contributing to the large positive joint force power at the hip of the stance leg. These hip joint force powers assisted in motion recovery during sprinting. In conclusion, the lumbosacral torsional torque might contribute to the recovery motion in sprinting through application of the anterior–posterior joint forces at the hip joints via pelvic rotation.     

The sidestep cutting manoeuvre requires exertion of lumbosacral lateral flexion torque to avoid excessive pelvic obliquity

During sidestep cutting, the pelvis is supported only on one side; this affects the athlete’s posture. This study investigated the mechanism to avoid excessive pelvic obliquity during sidestep cutting. Ten physically active men performed sidestep cutting with maximal effort, and we captured the kinematics and kinetics with force platforms and an eight-camera motion capture system. Our results indicated that the stance hip exerted little abduction torque; however, lumbosacral lateral flexion torque was exerted towards the free-leg side (peak value: 3.39 ± 0.91 N m/kg). Although bilateral hip joint forces acted to drop the free-leg side of the pelvis, the net torque around pelvic elevation/drop axis was nearly zero during the entire stance phase and the change in the angular momentum around the pelvic elevation/drop axis from touchdown to toe-off was negligible (?0.004 ± 0.003 N m s/kg). The integrated components of lateral flexor for elevating the free-leg side of the pelvis (0.220 ± 0.072 N m s/kg) were significantly larger than any other integrated components, which were all negligible (<0.010 N m s/kg). Thus, sidestep cutting requires the lumbosacral lateral flexion torque exertion to neutralise the passive action that drops the free-leg side of the pelvis.     

Kinetics and kinematics analysis of incremental cycling to exhaustion

Technique changes in cyclists are not well described during exhaustive exercise. Therefore the aim of the present study was to analyze pedaling technique during an incremental cycling test to exhaustion. Eleven cyclists performed an incremental cycling test to exhaustion. Pedal force and joint kinematics were acquired during the last three stages of the test (75%, 90% and 100% of the maximal power output). Inverse dynamics was conducted to calculate the net joint moments at the hip, knee and ankle joints. Knee joint had an increased contribution to the total net joint moments with the increase of workload (5–8% increase, p < 0.01). Total average absolute joint moment and knee joint moment increased during the test (25% and 39%, for p < 0.01, respectively). Increases in plantar flexor moment (32%, p < 0.01), knee (54%, p < 0.01) and hip flexor moments (42%, p = 0.02) were found. Higher dorsiflexion (2%, for p = 0.03) and increased range of motion (19%, for p = 0.02) were observed for the ankle joint. The hip joint had an increased flexion angle (2%, for p < 0.01) and a reduced range of motion (3%, for p = 0.04) with the increase of workload. Differences in joint kinetics and kinematics indicate that pedaling technique was affected by the combined fatigue and workload effects.     

Influence of foot-stretcher height on rowing technique and performance

Strength, technique, and coordination are crucial to rowing performance, but external interventions such as foot-stretcher set-up can fine-tune technique and optimise power output. For the same resultant force, raising the height of foot-stretchers on a rowing ergometer theoretically alters the orientation of the resultant force vector in favour of the horizontal component. This study modified foot-stretcher heights and examined their instantaneous effect on foot forces and rowing technique. Ten male participants rowed at four foot-stretcher heights on an ergometer that measured handle force, stroke length, and vertical and horizontal foot forces. Rowers were instrumented with motion sensors to measure ankle, knee, hip, and lumbar–pelvic kinematics. Key resultant effects of increased foot-stretcher heights included progressive reductions in horizontal foot force, stroke length, and pelvis range of motion. Raising foot-stretcher height did not increase the horizontal component of foot force as previously speculated. The reduced ability to anteriorly rotate the pelvis at the front of the stroke may be a key obstacle in gaining benefits from raised foot-stretcher heights. This study shows that small changes in athlete set-up can influence ergometer rowing technique, and rowers must individually fine-tune their foot-stretcher height to optimise power transfer through the rowing stroke on an ergometer.